This invention relates generally to closures for hollow structures and more particularly to a protective closure for hollow structures subject to high velocity rotation.
Heretofore, hollow structures used in turbine jet engines, gas turbines and high velocity rotors in the chemical fields and the dairy industries were subject to centrifugal forces which caused material failure and subsequent rupture of their protective closures. These ruptures sometimes create projectiles made up of ruptured pieces of the closure material which have caused extensive damage to adjoining structures. Additionally, such a rupture of a protective closure on a hollow tube or shaft used in, for example, a turbine can cause the loss of the dynamic balance of the turbine resulting in more damage to the turbine and adjoining structures.
Heretofore, protective closures when subjected to high velocities, expand and if the particular closure configuration is eliptical, material failures in the closure occur resulting in the damages described above. When these closures are rotated at high velocities they are subject to both axial stresses (centrifugal force) and hoop stresses. Axial stress generally occurs at the knuckle of the protective closure which is the weakest part of the closure. The loop stress occurs parallel to the longitudinal axis of the shaft, tangential to the wall of the shaft where the closure is coupled. This hoop stress creates bulges in the material of the closure resulting in further imbalance in the entire rotating system.
The metal material used to form these protective closures is basically shaped from rolled sheet material by any one of a number of processes well known in the art. These processes include formation by cold extrusion, hot extrusion, impact extrusion, hydraulic drawing and hydroforming. The protective closures of a single sheet of formed metal shaped by the previously described processes generally have a tendency for the material to attempt to regain or retake its original shape. This "memory" of the material is generally corrected by stress removing the material by the process of restriking or redrawing. But, in high velocity applications, since the memory of these formed materials is not completely destroyed, the formed materials have a tendency to flatten out, resulting in breakage, destortion and especially in high velocity applications, rupturing.